This invention relates generally to the field of electrical machinery. It relates more particularly to an electrical motor which utilizes a unique toroidal rotor/stator configuration providing a larger volume electromagnetic field interaction space and higher output torque than conventional cylindrical motors. The motor also has an inherent output speed reduction characteristic. It may also be operated in reverse by rotatably driving its output shaft from an external source, and thus function as an electrical generator.
Electrical motors consist of two basic machine parts--a stator, or stationary part, which typically defines a generally cylindrical internal cavity, and a rotor, or rotating part, which is also generally cylindrical in shape and which rotates about its central axis inside the stator cavity. Both the stator and the rotor typically have electromagnetic field-producing elements such as conductor windings through which electrical currents are passed. The rotor and stator are separated by a thin air gap. An output shaft is coaxially connected to the rotor so that it rotates with the rotor about the rotor axis.
In operation, a rotating electromagnetic field is set up across the tube-like air gap between the stator and rotor by energizing the windings on the stator or rotor or both with varying electrical signals. According to well-known principles of electromagnetic theory, the rotor and stator electromagnetic fields tend to line up, to minimize free potential energy, so that the center line of a north pole on one machine member (e.g. the rotor) is directly opposite the center line of a south pole on the other machine member (e.g., the stator). The tendency of the interacting fields to line up in this fashion produces the torque, or turning force, that rotates the rotor relative to the stator. The power output of the motor is proportional to the product of its torque and the rotational speed of its output shaft.
There are a wide variety of electrical motor designs, all having the same basic cylindrical rotor/stator configuration and all operating on the same basic electromagnetic principles, but each generally having different performance characteristics. For example, there are a-c motors which involve the supply of alternating electrical current to the windings of at least one of the stator and rotor. There are also d-c motors which involve the supply only of direct electrical current to the stator and/or rotor windings. A-C motors, in turn, may be synchronous, induction-type, single phase or polyphase, depending upon the particular manner in which input current signals are supplied. Similarly, d-c motors may be series-type, shunt-type or compound, depending upon the manner in which the rotor and stator windings are interconnected. Even these motor classifications often have sub-classifications. For example, a-c polyphase motors may be either Y- or .DELTA.-connected, depending upon how the windings for each phase are interconnected.
Selecting the right type of electrical motor for a given application depends to a large degree on the conditions within the mechanical equipment that the motor is intended to drive. For example, some applications require a motor speed which remains substantially constant as load varies, while others require an absolutely constant speed that is adjustable over a range. In still other applications, the torque which the motor is capable of supplying while starting, and the maximum torque which it can furnish while running, are factors of prime importance. Each of the different types of electrical motors that exist have different torque, speed and power characteristics which a user can seek to match to the particular requirements of the driven equipment application. When properly matched to the load, all of these motors generally operate at relatively high efficiencies.
Like all electromechanical devices, however, electrical motors have physical limitations which make it difficult to achieve a proper match to the driven equipment requirements in all cases. One of the most fundamental limitations in all electrical motor designs derives from the basic fact that the torque and power output of a motor are dependent upon the physical size of the electromagnetic field interaction space defined by the motor's rotor and stator. The motor designer who requires higher power output and/or higher torque with a particular type of motor generally achieves this by using a larger volume cylindrical rotor/stator configuration. In other words, the designer simply makes the motor with a larger diameter and/or longer rotor/stator. This approach is due principally to the fact that cylindrical rotors and straight, coaxially-positioned rotor output shafts have been considered axiomatic in electrical motor design since very early on in their practical development.
Similar approaches are used in the design of electrical generators, which are functionally and structurally basically the same as electrical motors except that the rotor in a generator is driven in rotation from an external source and the interacting electromagnetic fields are used to generate electricity. With electrical generators as well, higher power outputs and higher torques are conventionally achieved by using larger diameter and/or longer rotor/stator structures.